The present invention concerns the use of a numerically controlled "bar-type" horizontal boring mill to machine complex internal and external contours of generally circular cross-section which could hitherto be machined only on a numerically controlled lathe. In addition, straight and tapered thread chasing with a single point tool may be performed. These are accomplished using a cross-feed head which is powered by an existing numerically controlled spindle bar to vary the cutting radius of a rotating cutting tool, whereby powered numerical control of the tool radius is achieved. Feed is accomplished by moving the workpiece supporting table toward the cutting tool. The primary advantages of the present invention are that such contours and/or threads may be machined without rotating the workpiece, a particularly significant advantage when dealing with large workpieces and/or workpieces having a plurality of areas requiring machining, and that such contours and/or threads can be machined by users of "bar-type" horizontal boring mills who do not have an available numerically controlled lathe.
Although it has been known in the past to provide boring mills with cross-feed heads for performing facing operations, or for varying the diameter of bored holes, or for simultaneously boring and facing different surfaces of a workpiece, insofar as applicant is aware no one has ever actuated a cutting tool in a radial direction under numerical control, much less by using an existing fully powered numerically controlled spindle bar on a horizontal boring mill to actuate a cross-feed head to vary the radius of a cutting tool during the cutting operation. The substantial advantage of using the spindle bar is that it is a rugged duty machine component designed with sufficient strength to perform heavy machining operations rapidly. The use of an existing numerically controlled spindle bar to vary the radius of a cutting tool during machining permits the machine to advance, perform machining operations and retract as fast, and with the same strength, as the machine tool is designed to perform these operations during conventional machining.
With respect to the forming of threads using a horizontal boring mill, it is known to operate the machine in a milling mode using a milling cutter to form the threads. In such an operation the workpiece and cutter are moved relative to each other on two axes using numerically controlled circular interpolation, with feed being provided by movement of either the spindle bar or the workpiece supporting table. The present invention provides numerous advantages over this technique; specifically, an expensive special purpose cutter is not required, the programming is much simpler, the operation is performed much faster, and a better finish is obtained.
These and other features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.